Lymphokines are substances produced by lymphocytes and monocytes that have important functions in lymphoid cell interactions and regulation. One lymphokine, IL-1, was previously found to be produced by monocytes and macrophages. Recently, however, epidermal keratinocytes were also found to be able to produce IL-1. Since ultraviolet irradiation (UV) was found to have deleterious effects on several immune functions, both in vivo and in vitro, we investigated the effects of UV on IL-1 production by keratinocytes in vitro and in vivo and in normal and malignant macrophages in vitro. Contrary to our expectations, UV induced increased production of IL-1 in all these experiments. These results do not support the idea that the UV induced defect produced in antigen presenting cells is the result of decreased IL-1 production. Increased IL-1 production by keratinocytes after UV may also have important systemic consequences.